The present invention relates to a method for controlling a vehicle that comprises an engine arranged to drive at least one pair of half shafts and to drive at least one pump which is arranged to supply a hydraulic system comprising at least one hydraulic component with hydraulic oil, according to which method the power consumed by the hydraulic system is determined, the determined consumed power is compared with a reference value, and if the detected consumed power exceeds the reference value, the maximum available power for the hydraulic system is limited.
The invention also relates to a computer program for performing the method and to a device for controlling a vehicle.
The vehicle preferably comprises a working machine, such as a wheel-mounted loader, or a dumper.
There is a desire to reduce the emissions from diesel engines. This desire is driven not least by increasingly stringent legislation. A consequence of this is that a number of engines have too low a torque at low engine speeds. A mechanical loader, with a torque converter in the drive line and a hydraulic system for supplying among other things the lifting and tilting cylinders of the loader's loading unit and shovel and control cylinders for the steering, requires high torque even at low engine speeds. If the driver utilizes the power from the engine at low engine speeds to drive the vehicle's half shafts at the same time as the hydraulic system is activated, then there is a danger that the engine will cut out or that the engine will “stick”, that is it will not be able to increase the engine speed when the driver depresses the accelerator pedal. The driver can, of course, adjust the power consumption via various controls, but this can be problematical, particularly when the engine suddenly cuts out.
In U.S. Pat. No. 5,996,701 a control device is described for a working vehicle which is equipped with a hydraulic system for operating a piece of equipment, for example a shovel, and for turning the vehicle. The control device is intended to prevent the engine cutting out during operation. A first hydraulic pump is driven by the vehicle's engine and is arranged to raise or lower the piece of equipment. A second hydraulic pump with variable displacement is also driven by the vehicle's engine and is arranged to turn the body of the vehicle.
A load on the piece of equipment is detected and when the load exceeds a predetermined value, the maximum displacement for the second pump is reduced. By this means, the load is reduced which arises from the turning of the vehicle and the engine is prevented from cutting out. In other words, the handling of the vehicle's piece of equipment is given priority over the steering of the vehicle, by the displacement of the second pump being reduced.
It is desirable to achieve a method for controlling a vehicle which solves the problem of the engine cutting out and which makes possible more cost-effective operation and/or a more cost-effective system.
According to an aspect of the present invention, power limitation is carried out by the maximum available movement of at least one flow-regulating valve in the hydraulic system being limited. By a limited movement of the valve is meant that it can only be moved a certain limited amount, or in other words that the opening for the through-flow of the hydraulic oil is limited. In the existing hydraulic system of the working vehicle, there is already a plurality of movable flow-regulating valves. By controlling one or more of these, it is possible to achieve a cost-effective system/vehicle in a simple way. The flow-regulating valve can, for example, comprise a directional valve.
According to an aspect of the invention, the consumed power is determined by a flow being determined that is supplied from the pump, and in particular to the hydraulic component, and by the determined flow value being multiplied by a special pressure value, with the product giving a value for the consumed power. The determination of the flow and the pressure value can be carried out in a plurality of more or less accurate ways.
According to an aspect of the invention, a movement is detected of a first movable control means, such as a control lever, which is arranged to regulate the hydraulic component, and the size of the movement is utilized to determine the flow value to the component. More specifically, the signal from the control lever is sent to a computer unit and processed there, after which the computer unit sends a signal to the flow-regulating valve to control this. This is particularly advantageous when the hydraulic system is of a so-called load-detecting type. With such a load-detecting system, the pressure drop across a valve is in principle constant, which means that the flow is only dependent upon the movement of the movable control means.
According to a further aspect of the invention, the pressure is measured in the flow that is supplied to the hydraulic component, and the measured pressure is utilized as the special pressure value for the determination of the consumed power. According to an alternative embodiment, a pressure value is utilized which is characteristic of the hydraulic component. According to yet another alternative embodiment, the pressure value is changed depending upon the operational application. In addition, an estimated average value can be utilized for several different hydraulic components or operational applications.
It is also desirable to achieve a device for controlling a vehicle that solves the problem of the engine cutting out and that makes possible more cost-effective operation and/or a more cost-effective system/vehicle.
According to an aspect of the invention, a device for controlling a vehicle is provided. The device comprises a hydraulic system comprising at least one pump which is arranged to supply at least a first hydraulic component with hydraulic oil, the pump being connected to the vehicle's engine for driving the pump, the device comprising means for determining the power consumed by the hydraulic system, means for comparing the determined consumed power with a reference value, and means for limiting the maximum available power for the hydraulic system, the power-limiting means comprising a flow-regulating valve in the hydraulic system.
According to an aspect of the invention, the device comprises a computer unit which comprises software for the determination of the power consumed by the hydraulic system and the comparison of the determined consumed power with a reference value, and comprises the computer unit being connected to the first flow-regulating valve.